[geeks] Virtual Hosting, with a twist

[Eric Railine]

On 7/4/07, James Fogg <James at jdfogg.com> wrote:
> I work for a company that has, among other products, a network device
> management tool. It "talks" to network devices on the usual ports,
> telnet, ssh, snmp, tftp etc. When we've had clients try to run our
> product on a VMWare instance the performance goes in the toilet.
>
> Our application is pretty light weight (as light weight as a Java app
> can be anyways). After some experimentation we've found that it's when
> we reach out to the network devices (up to 200 at a time) we kill VMWare
> performance. It appears to be something related to how VMWare handles
> its network stack. Dropping the connection limit down to 20 doesn't
> bring back a whole lot of performance.

Interesting.  That's not been typical of my experience with ESX over
the last several years.  Even on older hardware (4-5 years old now)
with sufficient RAM & dual CPUs we've easily run ~10 guests
concurrently without issue - including Windows domain controllers,
DHCP, DNS, and/or WINS servers, database servers, network
mgmt/monitoring servers, Citrix/Windows terminal servers, etc.  I
don't have a good guess at how many concurrent network connections
were active on an individual guest (peak or average), but it's
certainly been more than 20 at peak, and more than 200 for all guests
on the ESX host.  Even running 4+ guests on an older 2-disk RAID1
VMware Server (not ESX) has shown perfectly acceptable performance.

In my experience the biggest factors affecting performance under ESX
are I/O, RAM, CPU, then network (in that order).  I haven't personally
seen any app that 'couldn't' be virtualized successfully; I'm curious
what the root issue was with your application.

-Eric